The present invention relates to an emergency control system for elevators, and more particularly to a control system for elevators suitable for regulating the operation of the elevators while an earthquake occurs.
During an earthquake-operation for elevators proposed heretofore, upon detection of an occurrence of an earthquake, the cage of an elevator is driven to stop at the nearest floor, the door is opened and thereafter the operation of the elevator is suspended. In one of such conventional earthquake-operations, an initial slight vibration caused by an earthquake is detected to immediately stop the cage at the nearest floor and make passengers take refuge prior to the occurrence of a strong vibration of the earthquake. However, the detector for detecting an initial slight vibration operates in response to relatively weak vibration so that the elevator is not subjected to damage. Therefore, there arises a problem that the elevator may be undesirably driven into an earthquake-operation by a vibration not resulting from an earthquake.
Of the control systems proposed heretofore, there is known a control system disclosed for example in Japapense Patent Unexamined Publication No. 55-106980, wherein the system comprises first and second detectors responsive respectively to big and small vibrations; a first circuit responsive to the first detector for conducting a predetermined, preliminary earthquake-operation for a predetermined time interval; and a second circuit responsive to the second detector for conducting a predetermined, main earthquake-operation; wherein the first circuit is disabled during the predetermined time interval so as not to be responsive to the first detector.
With the control system as above, however, if a big earthquake does not occur there also arises a problem: since the first circuit is enabled after the lapse of the predetermined time interval, the first detector responds to a slight main earthquake (which is not sufficiently strong for actuating the second detector) which may occur after the initial, slight vibration. As a result, the first circuit is initiated to again conduct a preliminary earthquake-operation, thereby resulting in repetitive stoppages of the elevator.